The present invention is directed to a neck ring mechanism for transferring one or more preforms, also known as blanks or parisons, from the blank mode section of an I.S. machine to the blow mold section. The mechanism transfers the neck mold holder arms over 180.degree. so as to perform the invert function.
Neck ring mechanisms are well-known in the art. For example, U.S. Pat. No. 3,762,907 issued to Quinn et al. provides a general description of such a mechanism wherein a molten glass gob is delivered to the blank mold section of the I.S. machine. The molten gob is subjected to an air discharge so as to force the molten glass into a split neck mold and around a plunger. The plunger is then retracted, and counter blow air is introduced into the depression left by the plunger so as to form a parison. The neck ring mechanism then transfers the parison to the blow mold section, inverting the parison in the process so that the mouth of the parison is supported by the neck mold. The neck mold sections are then separated so that the parison is left hanging in the blow mold. The neck mold holder arms are returned 180.degree. to the blow mold section, and the parison is reheated and blown to final shape in the blow mold section.
A particular neck ring mechanism for performing this function is described in U.S. Pat. No. 2,072,444 issued to Rowe. The mechanism described in that patent includes a splined rock shaft and a pair of spaced cylinders which mate with the splined shaft so that the cylinders are reciprocable in opposite directions parallel to the shaft axis. Each neck mold holder arm is supported on a T-shaped track located on a cylinder outer surface. A piston is pinned to the rock shaft so as to seal the gap between the cylinders and form an air chamber therebetween. Air is introduced in the chamber through an axial bore in the rock shaft so as to move the cylinders in opposite directions against associated bias springs. As the cylinders move apart, the neck mold holder arms move apart and the neck mold sections separate thereby releasing the parison. The invert function is accomplished by a rack driven gear coupled to the rock shaft. The gear is oscillated by the rack so as to transfer the neck mold support arms back and forth over 180.degree. between the blank mold and blow mold sections of the machine.
Misalignment of the cylinders due to backlash is a recurring problem at the neck ring mechanism. Thus, backlash between the cylinders and th splined rock shaft produces a rotational misalignment of the cylinders and corresponding misalignment of the neck molds. The problem worsens as the shaft splines wear.
Moreover, the splined rock shaft and piston assembly permit objectionable air leakage between the cylinders which may result in incomplete opening of the neck molds. As the shaft splines wear, this problem also worsens.
It is an object of the present invention to provide a neck ring mechanism wherein the cylinder backlash can be easily compensated.
Another object of the invention is to provide a neck ring mechanism wherein air leakage between the cylinders is substantially eliminated.
Other objects and advantages of the invention appear hereinafter in the following disclosure.